Spreading code sequences for reference signals

ABSTRACT

Methods, systems, and devices related to applying a spreading code to reference signals are described. In one exemplary aspect, a method for wireless communication includes receiving a message indicating a set of control options available to the mobile device for data transmissions. The method includes selecting a spreading code sequence from a number of spreading code sequences, wherein the spreading code sequence corresponds to a control option in the set of control options, wherein the number of spreading code sequences is greater than a length of each of the spreading code sequence, and wherein the spreading code sequences are generated using a method when the length of each of the spreading code sequences is greater than or equal to a value. The method also includes generating a plurality of reference signal symbols using the spreading code sequence, and transmitting the plurality of reference signal symbols.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent document is a continuation of and claims benefit of priorityto International Patent Application No. PCT/CN2017/118059, filed on Dec.22, 2017. The entire content of the before-mentioned patent applicationis incorporated by reference as part of the disclosure of thisapplication.

TECHNICAL FIELD

This patent document is directed generally to digital wirelesscommunications.

BACKGROUND

Mobile communication technologies are moving the world toward anincreasingly connected and networked society. The rapid growth of mobilecommunications and advances in technology have led to greater demand forcapacity and connectivity. Other aspects, such as energy consumption,device cost, spectral efficiency, and latency are also important tomeeting the needs of various communication scenarios. Varioustechniques, including new ways to provide higher quality of service, arebeing discussed.

SUMMARY

This document discloses methods, systems, and devices related to digitalwireless communication, and more specifically, to techniques related tospreading code generation and applying the generated spreading code(s)to reference signals for pre-configured or grant-free transmissions.

In one exemplary aspect, a method for wireless communication isdisclosed. The method includes receiving, at a mobile device, a messageindicating a set of control options available to the mobile device fordata transmissions; selecting a spreading code sequence from a number ofspreading code sequences, wherein the spreading code sequencecorresponds to a control option in the set of control options, whereinthe number of spreading code sequences is greater than a length of eachof the spreading code sequence, and wherein the spreading code sequencesare generated using a first method when the length of each of thespreading code sequences is greater than or equal to a value; generatinga plurality of reference signal symbols using the spreading codesequence; and transmitting, from the mobile device, the plurality ofreference signal symbols.

In some embodiments, the first method includes generating the spreadingcode sequences using a Fourier Transform matrix of dimension N and apermutation of ones and zeros that includes M=1+C_N{circumflex over( )}1+C_N{circumflex over ( )}2+ . . . +C_N{circumflex over ( )}(N−2)vectors, each vector having a length of N. In some implementations, thevalue is equal to 3.

In some embodiments, the spreading code sequences are generated using asecond method different from the first method when the length of each ofthe spreading code sequence is less than the value. The second methodincludes generating the spreading code sequences by combining 1 and aset of primitive Nth roots of unity, N being in a range from 1 to thenumber of spreading code sequences.

In some embodiments, the set of control options include information ofmodulation and code schemes, redundancy version, or hybrid automaticrepeat request (HARM) process index for data transmissions. In someembodiments, the number of spreading code sequences is equal to orgreater than a number of control options.

In another exemplary aspect, a method for wireless communication isdisclosed. The method includes receiving, at a mobile device, a messageindicating one or more parameters and a number of spreading codesequences for data transmissions, wherein the spreading code sequencesare generated using a first method when the length of each of thespreading code sequences is greater than or equal to a value; generatinga reference signal sequence using the one or more parameters and aspreading code sequence from the spreading code sequences, wherein thenumber of spreading code sequences is greater than the length of each ofthe spreading code sequence; and transmitting, from the mobile device,the reference signal sequence.

In some embodiments, the first method includes generating the spreadingcode sequences using a Fourier Transform matrix of dimension N and apermutation of ones and zeros that includes M=1+C_N{circumflex over( )}1+C_N{circumflex over ( )}2+ . . . +C_N{circumflex over ( )}(N−2)vectors, each vector having a length of N. In some implementations, thevalue is equal to 3.

In some embodiments, the spreading code sequences are generated using asecond method different from the first method when the length of each ofthe spreading code sequence is less than the value. The second methodincludes generating the spreading code sequences by combining 1 and aset of primitive Nth roots of unity, N being in a range from 1 to thenumber of spreading code sequences.

In some embodiments, the one or more parameters indicate a number ofZadoff-Chu roots or a number of cyclic shifts. In some implementations,generating the reference signal further comprises generating a legacyreference signal symbol using the one or more parameters; obtaining alegacy reference signal sequence by repeating the legacy referencesignal symbol for N times, wherein N is the length of each of thespreading code sequence; selecting the spreading code sequence from thespreading code sequences; and multiplying, element-by-element, thelegacy reference signal sequence with the spreading code sequence toobtain the reference signal sequence.

In some embodiments, the one or more parameters indicate a legacyreference signal sequence. In some implementations, generating thereference signal further comprises selecting the spreading code sequencefrom the spreading code sequences; and multiplying, element-by-element,at least a part of the legacy reference signal sequence with thespreading code sequence to obtain the reference signal sequence.

In another exemplary aspect, a method for wireless communication isdisclosed. The method includes transmitting, to a mobile device, amessage indicating a set of control options available to the mobiledevice for data transmissions; and receiving, from the mobile device, aplurality of reference signal symbols, wherein the plurality ofreference signal symbols is generated using a spreading code sequenceselected from a number of spreading code sequences, wherein thespreading code sequence corresponds to a control option in the set ofcontrol options, wherein the number of spreading code sequences isgreater than a length of each of the spreading code sequence, andwherein the spreading code sequences are generated using a first methodwhen the length of each of the spreading code sequences is greater thanor equal to a value.

In some embodiments, the first method includes generating the spreadingcode sequences using a Fourier Transform matrix of dimension N and apermutation of ones and zeros that includes M=1+C_N{circumflex over( )}1+C_N{circumflex over ( )}2+ . . . +C_N{circumflex over ( )}(N−2)vectors, each vector having a length of N. In some implementations, thevalue is equal to 3.

In some embodiments, the spreading code sequences are generated using asecond method different from the first method when the length of each ofthe spreading code sequence is less than the value. The second methodincludes generating the spreading code sequences by combining 1 and aset of primitive Nth roots of unity, N being in a range from 1 to thenumber of spreading code sequences.

In some embodiments, the set of control options include information ofmodulation and code schemes, redundancy version, or hybrid automaticrepeat request (HARM) process index for data transmissions. In someembodiments, the number of spreading code sequences is equal to orgreater than a number of control options.

In another exemplary aspect, a method for wireless communication isdisclosed. The method includes transmitting, to a mobile device, amessage indicating one or more parameters and a number of spreading codesequences for data transmissions, wherein the spreading code sequencesare generated using a first method when the length of each of thespreading code sequences is greater than or equal to a value; andreceiving, from the mobile device, a reference signal sequence, whereinthe reference signal sequence is generated using the one or moreparameters and a spreading code sequence from the spreading codesequences, and wherein the number of spreading code sequences is greaterthan the length of each of the spreading code sequence.

In some embodiments, the first method includes generating the spreadingcode sequences using a Fourier Transform matrix of dimension N and apermutation of ones and zeros that includes M=1+C_N{circumflex over( )}1+C_N{circumflex over ( )}2+ . . . +C_N{circumflex over ( )}(N−2)vectors, each vector having a length of N. In some implementations, thevalue is equal to 3.

In some embodiments, the spreading code sequences are generated using asecond method different from the first method when the length of each ofthe spreading code sequence is less than the value. The second methodincludes generating the spreading code sequences by combining 1 and aset of primitive Nth roots of unity, N being in a range from 1 to thenumber of spreading code sequences.

In some embodiments, the one or more parameters indicate a number ofZadoff-Chu roots or a number of cyclic shifts. In some embodiments, theone or more parameters indicate a legacy reference signal sequence.

In another exemplary aspect, a wireless communications apparatuscomprising a processor is disclosed. The processor is configured toimplement a method described herein.

In yet another exemplary aspect, the various techniques described hereinmay be embodied as processor-executable code and stored on acomputer-readable program medium.

The details of one or more implementations are set forth in theaccompanying attachments, the drawings, and the description below. Otherfeatures will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an exemplary uplink signal incurrent Long Term Evolution (LTE) systems.

FIG. 2 shows a schematic diagram of signal modulation according to theWiFi 802.11 standards.

FIG. 3 is a flowchart representation of a method for wirelesscommunication.

FIG. 4 is a flowchart representation of another method for wirelesscommunication.

FIG. 5 is a flowchart representation of another method for wirelesscommunication.

FIG. 6 is a flowchart representation of another method for wirelesscommunication.

FIG. 7 shows an exemplary plot of the probability of multiple userequipment sharing the same resources.

FIG. 8 shows another exemplary plot of the probability of multiple userequipment sharing the same resources.

FIG. 9 shows an example of a wireless communication system wheretechniques in accordance with one or more embodiments of the presenttechnology can be applied.

FIG. 10 is a block diagram representation of a portion of a radiostation.

DETAILED DESCRIPTION

With the continuous development of wireless communication technologies,a wide range of wireless communication services are emerging. Thedevelopment of Internet of Things (IoT), for example, allows a hugeamount of small devices (e.g., sensors and/or appliances) to communicatein cellular networks. The network traffic from these small devices tendsto be sporadic and includes small data packages. Such traffic is quitedifferent from the traditional types of network traffic, such as voiceor data services.

One of the challenges posed by IoT communication is to achieve resourceefficiency while supporting massive connections. Because the IoT traffictends to be sporadic and the amount of data is small, control signalingto setup and/or release connections between user equipment (UE) and basestations (BS) may occupy more network resources than required resourcesfor data transmissions. As a result, control channels can become abottleneck in IoT transmissions. To reduce signaling overhead andachieve higher resource efficiency, two possible transmissionmechanisms—resource pre-configuration and grant-free transmission—can beutilized.

Resource pre-configuration means pre-arranging physical resources intime and/or frequency domain for a specific UE. For example,semi-persistent scheduling (SPS) has been used to support voicetransmission in the Long Term Evolution (LTE) networks (VoLTE).

In LTE systems, resource allocation information for the PhysicalDownlink Shared Channel (PDSCH) and/or the Physical Uplink SharedChannel (PUSCH) is carried by the Physical Downlink Control Channel(PDCCH). The amount Orthogonal Frequency Division Multiplex (OFDM)symbols allowed for the PDCCH, however, is limited. For example, only1-3 OFDM symbols are allowed per subframe to carry PDCCH information. Asa result, using the dynamic scheduling (i.e., a one-to-onecorrespondence between a PDCCH signaling and a PDSCH/PUSCH allocation),the number of UEs that can be concurrently supported is limited.

Semi-persistent scheduling (SPS) was introduced to address thislimitation. With SPS, a UE is pre-configured by the base station with aSPS Radio Network Temporary Identifier (SPS-RNTI). A resource isallocated using the SPS-RNTI (instead of typical C-RNTI) and aperiodicity (e.g., 200 ms). During SPS, the allocated resource is usedby the UE according to the pre-configured periodicity.

SPS is well suited to periodic communication, such as VoLTE, so thatmore UEs can be supported without increasing PDCCH resources. However,transmission parameters, such as Modulation and Coding Scheme (MCS), arefixed for a given SPS allocation. To guarantee an acceptable failurerate per transmission, conservative modulation and coding schemes aregenerally used. Therefore, when channel conditions change, a new SPSallocation is needed. Furthermore, any incremental redundancyre-transmissions (e.g., Hybrid Automatic Repeat reQuest (HARQ) basedre-transmissions) will be separately scheduled using dynamic scheduling.Thus, SPS is not so efficient for IoT traffic because its periodicitycan be too long for a fixed MCS, leading to low resource efficiency.Dynamic scheduling of HARQ may also be too costly.

Grant-free transmission, on the other hand, originates from the ALOHAmethod in Ethernet communication. The ALOHA method allows multiple UEsto transmit using the same frequency resources. When collision happens,each collided UE chooses a random delay for re-transmission. An improvedALOHA method, also known as Slotted ALOHA (S-ALOHA), allows UEs to sharea common transmission period and a common start time to start theirtransmissions. Using the S-ALOHA method, the chance of collision can bereduced by half as compared with the traditional ALOHA method.

For wireless communication systems under a centric control by the BS,periodic downlink (DL) broadcast from the B S enables UEs to synchronizetheir uplink (UL) transmissions, thereby facilitating the usage ofS-ALOHA. Theoretically, the maximum channel utilization for S-ALOHA ise⁻¹, or about 37%. However, for IoT scenarios with a massive amount ofconnections (e.g., ˜10⁶ connections per km²), the efficiency andstability of the S-ALOHA method becomes questionable due to severe datapackage collisions, leading to low resource efficiency or even worse,malfunction of the whole system.

To improve resource efficiency of the S-ALOHA method, variousnon-orthogonal multiple access (NOMA) schemes have been proposed toallow UEs to share the same time-frequency resources. However, collisionavoidance and demodulation of reference signals are still the key issuesto address in order to ensure good reception (i.e., accurate channelestimation) for NOMA schemes. For example, in LTE systems, 64 preamblesare provided per cell for Random Access Channels (RACH). If a largeamount of UEs want to access the network using randomly selectedpreambles, the collision probability increases rapidly as the number ofUEs increases. For IoT applications with a massive number ofconnections, it is thus desirable to have a much larger reference signalpool to allow accurate UE detection and channel estimation withsimultaneous UEs transmissions.

In current systems, the reference signal pool may be limited. FIG. 1shows a schematic diagram of an exemplary uplink signal in current LTEsystems. The uplink signal 100 includes two reference signal (RS)symbols 101 to facilitate channel estimation and physical impairmentmeasurement. There is no spreading code applied to these referencesignal symbols. FIG. 2 shows a schematic diagram of signal modulationaccording to the WiFi 802.11 standards. In 802.11a/g/n/ac systems, acommon reference signal head—Non-HT Short Training Field (L-STF) 201 andNon-HT Long Training Field (L-LTF) 202—is added before control and datato enable UE detection and channel estimation. There are ten identicalsymbols in L-STF (short) and two identical symbols in L-LTF (long)respectively. The symbols in the reference signal are simply repeated.In a way, the repetition is equivalent to spreading with the referencesignal with a spreading code having all ones. However, such spreadingdoes not greatly increase the amount of available reference signals.

This patent document describes the generation of a spreading code setand methods of applying the spreading code set to reference signals toobtain a larger pool of reference signals. By having a larger pool ofreference signals, control information may be conveyed as a part ofreference signal transmission without incurring any signaling overhead.A larger reference signal pool also reduces the probability of UE datacollisions in grant-free transmissions, thereby increasing resourceefficiency for IoT scenarios.

Spreading Code Generation

An orthogonal spreading code set, such as an N×N code matrix, may spreada reference signal having N symbols into a pool of N reference signals.However, when N is a small value (e.g., 2 or 3), the pool is still toosmall to effectively carry control information or reduce transmissioncollisions. Therefore, it is desirable to use a non-orthogonal spreadingcode set, such as a code matrix having M entries (M>>N), to ensure thatthe reference signal can be sufficiently spread. Details regarding thegeneration of the spreading code are described as follows.

Length-2 Codebook

A length-2 codebook can be applied to reference signals that have alength of 2 (i.e., N_(code)=2).

The full code set is given by [1 1; 1 ω; . . . ; 1 ω²; . . . ; 1ω^(M-1)], wherein

${\omega = e^{j\frac{2\pi}{M}}},$

and M>N_(code). The value of M can be determined based on the number ofcontrol options (N_(option)) available to the UE, which will bediscussed in connection with FIGS. 3-4. The value of M can also bedetermined by the desirable side of the reference signal pool. In someembodiments, both the BS and the UE can store a subset of the full codeset.

Length-3 Codebook

A length-3 codebook can be applied to reference signals that have alength of 3 (i.e., N_(code)=3).

The length-3 codebook can be generated using the following steps:

1.1: Prepare a base code set given by a Fourier Transform matrix [1 1 1;1 ω ω²; 1 ω² ω⁴], where

$\omega = {e^{j\frac{2\pi}{3}}.}$

1.2: Prepare a spreading code matrix given as [1 1 1; 1 1 0; 1 0 1; 0 11].

1.3: Select an entry from the base code set (e.g., [1 ω ω²]). Selectanother entry from the spreading code matrix (e.g., [1 0 1]). Perform anelement-to-element multiplication using these two entries to obtain anew entry of the code set (e.g., [1 0 ω²]). Perform this step for allentries in the base code set and the spreading code matrix to obtain afull code set.

The full code set includes 12 entries, which are: [1 1 1; 1 ω ω²; 1 ω²ω⁴; 1 1 0; 1 ω 0; 1 ω² 0; 1 0 1; 1 0 ω²; 1 0 ω⁴; 0 1 1; 0 ω ω²; 0 ω²ω⁴].

Length-4 Codebook

A length-4 codebook can be applied to reference signals that have alength of 4 (i.e., N_(code)=4).

The length-4 codebook can be generated using the following steps:

2.1: Prepare a base code set given by a Fourier Transform matrix [1 1 11; 1 ω ω² ω³; 1 ω² ω⁴ ω⁶; 1 ω³ω⁶ ω⁹], where

$\omega = {e^{j\frac{2\pi}{4}}.}$

2.2: Prepare a spreading code matrix given as [1 1 1 1; 1 1 1 0; 1 1 01; 1 0 1 1; 0 1 1 1; 0 0 1 1; 0 1 1 0; 1 1 0 0; 1 0 0 1; 1 0 1 0; 0 1 01].

2.3: Select an entry from the base code set (e.g., [1 ω ω² ω³]). Selectanother entry from the spreading code matrix (e.g., [1 0 1 1]). Performan element-to-element multiplication using these two entries to obtain anew entry of the code set (e.g., [1 0 ω² ω³]). Perform this step for allentries in the base code set and the spreading code matrix to obtain afull code set.

The full code set includes 4×11=44 entries.

Length-N Codebook

The generation method used for length-3 and length-4 codebook can begeneralized and applied to length-N, wherein N_(code)>2. A length-Ncodebook can be applied to reference signals that have a length of N(i.e., N_(code)=N).

The length-N codebook can be generated using the following steps:

2.1: Prepare a base code set given by a Fourier Transform matrix havinga dimension N, where

${\omega = e^{j\frac{2\pi}{N}}}.$

2.2: Prepare a spreading code matrix. The spreading code matrix isgenerated using (1) one length-N vector including all ones, (2) C_(N) ¹number of length-N vectors, each having N−1 ones and 1 zero (3) C_(N) ²number of length-N vectors, each having N−2 ones and 2 zero, . . . , and(N−1) C_(N) ^(N-2) number of length-N vectors, each having 2 ones andN−2 zero. The number of entries in the spreading code matrix is given byM=1+C_(N) ¹+C_(N) ²+ . . . +C_(N) ^(N-2).

2.3: Select an entry from the base code set. Select another entry fromthe spreading code matrix. Perform an element-to-element multiplicationusing these two entries to obtain a new entry of the code set. Performthis step for all entries in the base code set and the spreading codematrix to obtain a full code set.

The full code set includes M entries (M>N), each entry having a lengthof N.

Resource Pre-Configuration

The spreading code as discussed above can be applied to referencesignals in resource pre-configuration scenarios to carry controlinformation such as Modulation and Coding Schemes (MCS), RedundancyVersion (RV) and/or HARQ process index.

FIG. 3 is a flowchart representation of a method for wirelesscommunication. The method 300 includes, at 302, transmitting, to amobile device, a message indicating a set of control options availableto the mobile device for data transmissions. The method also includes,at 304, receiving, from the mobile device, a plurality of referencesignal symbols.

In the pre-configuration stage (e.g., in SPS configuration for a targetUE), the base station can inform the UE of the available control optionsfor MCS, RV, and/or HARQ process index. The number of available optionsis denoted as N_(option). A spreading code set with M entries is storedby the BS, wherein M>=N_(option). In some embodiments, M=N_(option) andan one-to-one mapping between the control options and the spreadingcodes can be established and/or stored by the base station. In someembodiments, M>N_(option), and the base station may choose to use only apart of the spreading codes in the code set. For example, the BS mayselect a subset of the spreading codes from the code set according to apredefined rule. In some implementation, the predefined rule may limitthe selection of the spreading codes to the first N_(option) entries inthe complete code set, and the remaining M−N_(option) entries areconsidered to be reserved.

FIG. 4 is a flowchart representation of a method for wirelesscommunication. The method 400 includes, at 402, receiving, at a mobiledevice, a message indicating a set of control options available to themobile device for data transmissions. In some embodiments, the target UEreceives available control options from the base station via PDCCH. Thecontrol options can include a combination of MCS, RV, and/or HARQprocess index according to channel status and/or previous transmissionstatus. The target UE may also store the spreading code set with Mcodes, wherein M>=N_(option).

The method 400 includes, at 404, selecting a spreading code sequencefrom a number of spreading code sequences, wherein the spreading codesequence corresponds to a control option in the set of control options.It is noted that the number of spreading code sequences M is greaterthan the length of each of the spreading code sequence N_(code). In someembodiments, M=N_(option), so the UE uses the same one-to-one mappingbetween the control options and the spreading codes as the BS. In someembodiments, M>N_(option), and the UE may choose to use only a part ofthe spreading codes in the code set. For example, the UE may select asubset of the spreading codes from the code set according to the samepredefined rule used by the BS. In some implementation, the predefinedrule may limit the selection of the spreading codes to the firstN_(option) entries in the complete code set; the remaining M-N_(option)entries are considered to be reserved.

The method 400 includes, at 406, generating a plurality of referencesignal symbols using the spreading code sequence. The reference signalsymbols can be generated by multiplying, element by element, theoriginal reference signal with the spreading code sequence. The method400 also includes, at 408, transmitting, from the mobile device, theplurality of reference signal symbols.

The BS then receives the plurality of reference signal symbols from theUE. The BS uses its stored code set to match the code carried by thereference signal symbols. The matched code allows the BS to detect UE'scontrol option (e.g., MCS, RV and/or HARQ process index). The BS thenuses the detected control option to decode the data symbols from the UE.

Details of the techniques for resource pre-configuration scenarios arefurther described in the following embodiments.

Example Embodiment 1

A length-2 codebook with four entries is given by [1 1; 1 j; 1 −1; 1 −j](i.e., M=4). With this codebook, the reference signal carries controlinformation to indicate the MCS selected by UE. Table 1 shows an exampleof MCS options for a length-2 codebook.

TABLE 1 Exemplary MCS options for a length-2 codebook Code carried onreference signal Modulation Code rate [1 1] BPSK 1/2 [1 j] BPSK 1/3 [1−1] QPSK 1/2 [1 −i] QPSK 1/3

When the BS receives a reference signal from a given UE, it retrievesthe carried spreading code by correlating the two symbols of thereference signal. The retrieved code helps the BS properly decode anddemodulate data symbols.

Example Embodiment 2

A length-3 codebook with 12 entries is given by [1 1 1; 1 ω ω²; 1 ω² ω⁴;1 1 0; 1 ω 0; 1 ω² 0; 1 0 1; 1 0 ω²; 1 0 ω⁴; 0 1 1; 0 ω ω²; 0 ω² ω⁴],where

$\omega = {e^{j\frac{2\pi}{3}}.}$

With this codebook, the reference signal carries control information toindicate the MCS and RV selected by UE. Table 2 shows an example of MCSand RV options for a length-3 codebook.

TABLE 2 Exemplary MCS and RV options for a length-3 codebook Codecarried on reference signal Modulation Code rate RV [1 1 1] BPSK 1/2 0[1 ω ω²] BPSK 1/2 1 [1 ω² ω⁴] BPSK 1/2 2 [1 1 0] BPSK 1/3 0 [1 ω 0] BPSK1/3 1 [1 ω² 0] BPSK 1/3 2 [1 0 1] QPSK 1/2 0 [1 0 ω²] QPSK 1/2 1 [1 0ω⁴] QPSK 1/2 2 [0 1 1] QPSK 1/3 0 [0 ω ω²] QPSK 1/3 1 [0 ω² ω⁴] QPSK 1/32

When BS receives a reference signal from a given UE, it detects energyof the symbols and locates the possible zero-value symbol. The BS thenretrieves the carried spreading code by correlating the non-zero symbolsof the reference signal. The retrieved code helps the BS properly decodeand demodulate data symbols.

Example Embodiment 3

A length-2 codebook with 4 entries is given by [1 1; 1 j; 1 −1; 1 −j](i.e., M=4). With this codebook, the reference signal carries controlinformation to indicate HARQ process index selected by UE. Table 1 showsan example of HARQ process index options for a length-2 codebook.

TABLE 3 Exemplary HARQ process index options for a length-2 codebookCode carried on HARQ process reference signal index [1 i] 1 [1 j] 2 [1−1] 3 [1 −j] 4

When the BS receives a reference signal from a given UE, it retrievesthe carried spreading code by correlating the two symbols of thereference signal. The retrieved code helps the BS determine the HARQprocess index of current data part and facilitate possible HARQcombining with previous received data packages.

Grant-Free Transmission

In grant-free transmissions, a reference signal pool is provided to UEs.A UE randomly selects one of the reference signals and transmits italong with the data. The reference signal facilitates UE detection andchannel estimation on the base station side. In LTE systems, the RandomAccess Channel (RACH) is an example of the legacy reference signaldesign. The legacy reference signal pool includes one or more Zadoff-Chu(ZC) sequences with different roots N_(root) and cyclic shifts N_(cs).The number of available reference signal in a legacy reference signalpool is N_(rs)=N_(root)×N_(cs).

The spreading code as discussed above can be applied to the legacyreference signal pool in grant-free transmission scenarios to increasethe size of reference signal pool, thereby reducing the probability oftransmission collisions.

For example, a legacy reference signal has a length of L (i.e., thelegacy reference signal has L symbols). A spreading code can be chosenfrom the spreading code set to be applied to the legacy referencesignal. The spreading code length N_(code)<=L. If N_(code)=L, anelement-by-element multiplication is performed such that each element ofthe spreading code is applied to each symbol of the reference signal. IfN_(code)<L, a subset of the reference signal symbols is selected, basedon a predefined rule, to match the spreading code length. In someimplementations, the predefined rule may limit the selection ofreference signal symbols to be the first N_(code) symbols, leaving theremaining L−N_(code) symbols unchanged. Then, an element-by-elementmultiplication is performed such that each element of the spreading codeis applied to each symbol of the selected subset of reference signal.

As discussed above, using an orthogonal spreading code can spread areference signal into a pool of N_(code) reference signals, at the costof occupying N_(code) resources. The original pool ofN_(rs)=N_(root)×N_(cs), therefore, can be spread into a larger pool ofN′_(rs)=N_(root)×N_(cs)×N_(code). The use of non-orthogonal spreadingcodes can further expand the size of the reference signal pool. A newpool of N″_(rs)=N_(root)×N_(cs)×M can be generated, wherein M>N_(code).

FIG. 5 is a flowchart representation of a method for wirelesscommunication. The method 500 includes, at 502, transmitting, to amobile device, a message indicating one or more parameters and a numberof spreading code sequences for data transmissions. The method alsoincludes, at 504, receiving, from the mobile device, a reference signalsequence.

In a grant-free transmission scenario, the BS informs a group of UEs oftheir common reference signal configuration (including N_(root) andN_(cs)) in the common DCI configuration via PDCCH. The BS may alsoinform the group of UEs the spreading code pool that has M spreadingcode entries.

FIG. 6 is a flowchart representation of a method for wirelesscommunication. The method 600 includes, at 602, receiving, at a mobiledevice, a message indicating one or more parameters and a number ofspreading code sequences for data transmissions. In some embodiments, aUE in a group of UEs receives common DCI configuration from the BS. Thecommon DCI configuration includes parameters such as N_(root) and N_(cs)for generating a legacy reference signal. The common DCI configurationalso includes an indicator to indicate the spreading codebook pool thathas M codes. The UE is then able to generate a reference signal poolthat includes N″_(rs)=N_(root)×N_(cs)×M reference signals, whereinM>N_(code).

The method includes, at 604, generating a reference signal sequenceusing the one or more parameters and a spreading code sequence from thespreading code sequences. The reference signal can be generated asfollows:

3.1: Generate a legacy reference signal symbol using a selected root andcyclic shift.

3.2: Repeat the legacy reference signal symbol N_(code) times to obtaina legacy reference signal sequence.

3.3: Select a N_(code)-length spreading code from the codebook thatincludes M entries.

3.4: Perform an element-by-element multiplication of the repeated legacyreference signal sequence and the N_(code)-length spreading code toobtain a reference signal sequence.

Alternatively, the one or more parameters indicate a legacy referencesignal having a length of L. The reference signal can be generated asfollows:

4.1: If L=N_(code), perform an element-by-element multiplication of thelegacy reference signal and the N_(code)-length spreading code to obtaina reference signal sequence.

4.2: If L>N_(code), select a subset of the legacy reference signal. Thesubset of the legacy reference signal includes N_(code) symbols. Performan element-by-element multiplication of the subset and theN_(code)-length spreading code to obtain a reference signal sequence.

The method also includes, at 606, transmitting, from the mobile device,the reference signal sequence.

After receiving the reference signal sequence at the BS, the BS mayperform the following steps to assist UE detection and channelestimation.

Despreading:

BS may despread the reference signal sequence by (1) applying theconjugated N_(code)-length spreading code on N_(code) reference signalsymbols using an element-by-element multiplication, and (2) summing upthe N_(code) reference signal symbols.

Detection:

For each despread reference signal, the BS compares the signal energy onN_(root)×N_(cs) windows with a threshold. If the signal energy exceedsthe corresponding threshold, a flag indicating UE existence on thecorresponding code index, root, and cyclic shift is set to true.

Channel Estimation:

For each combination of root and cyclic shift with a true flag, channelestimation can be carried out for the strongest code indices.

Details of the techniques for grant-free transmission scenarios arefurther described in the following embodiments.

Example Embodiment 4

In this embodiment, a legacy LTE RACH-style sequence having a length of144 is generated using a length-139 cyclic-padded ZC sequence. A phaserotation sequence is generated to carry a specific cyclic shift. Withfour ZC roots (N_(root)=4) and cyclic shift resolution of 2π/16(N_(cs)=16), a legacy reference signal pool with 4×16=64 entries isobtained. A length-2 codebook (N_(code)=2) with 4 entries is given by [11; 1 j; 1 −1; 1 −j] (i.e., M=4, M>N_(code)). With this codebook, thesize of the legacy reference signal pool can be extended to 4×16×4=256entries. A UE can randomly select a combination of ZC root, cyclicshift, and a spreading code from the code set to generate its referencesignal symbols.

FIG. 7 shows an exemplary plot of the probability of multiple UEs (i.e.,K UEs) sharing the same resources. It is evident that, with an enlargedreference signal pool of 256 entries, the collision probability betweentwo UEs decreases from 15% to 4%. The collision probability betweenthree UEs decreases from 1.1% to 0.1%.

A given combination of ZC root and cyclic shift can indicate more thanone multiplexed UE. The BS, after receiving the reference signalsequence, coherently combines the two reference symbols with 4 spreadingcodes. Based on the four combining results, BS selects fewer than threespreading codes with largest combining energy and estimates propagationchannel for the hypothesized UEs. The rationale behind this selection isthat the probability of three UEs multiplexed on a given combination ofZC root and cyclic shift is very small (˜1%).

Example Embodiment 5

In this embodiment, a legacy LTE RACH-style sequence with length of 144is generated using a length-139 cyclic-padded ZC sequence. A phaserotation sequence is generated to carry a specific cyclic shift. Withfour ZC roots (N_(root)=4) and cyclic shift resolution of 2π/16(N_(cs)=16), a reference signal pool with 4×16=64 entries is obtained. Alength-3 codebook (N_(code)=3) with 12 entries is given by [1 1 1; 1 ωω²; 1 ω² ω⁴; 1 1 0; 1 ω 0; 1 ω² 0; 1 0 1; 1 0 ω²; 1 0 ω⁴; 0 1 1; 0 ω ω²;0 ω² ω⁴] (i.e., M=12, M>N_(code)). With this codebook, the size of thelegacy reference signal pool can be extended to 4×16×12=768 entries. AUE can randomly select a combination of ZC root, cyclic shift, and aspreading code from the code set to generate its reference signalsymbols.

FIG. 8 shows another exemplary plot of the probability of multiple UEs(i.e., K UEs) sharing the same resources. It is evident that, with anenlarged reference signal pool of 768 entries, the collision probabilitybetween two UEs decreases from 15% to 1%. The collision probabilitybetween three UEs decreases from 1.1% to 0.01%.

A given combination of ZC root and cyclic shift can indicate more thanone multiplexed UE. The BS, after receiving the reference signalsequence, coherently combines the three reference symbols with these 12spreading codes. Based on the 12 combining results, BS selects fewerthan four spreading codes with largest combining energy and estimatespropagation channel for the hypothesized UEs. The rationale behind thisselection is that the probability of four UEs multiplexed on a givencombination of ZC root and cyclic shift is very small (˜0.06%).

FIG. 9 shows an example of a wireless communication system wheretechniques in accordance with one or more embodiments of the presenttechnology can be applied. A wireless communication system 900 caninclude one or more base stations (BSs) 905 a, 905 b, one or morewireless devices 910 a, 910 b, 910 c, 910 d, and a core network 925. Abase station 905 a, 905 b can provide wireless service to wirelessdevices 910 a, 910 b, 910 c and 910 d in one or more wireless sectors.In some implementations, a base station 905 a, 905 b includesdirectional antennas to produce two or more directional beams to providewireless coverage in different sectors.

The core network 925 can communicate with one or more base stations 905a, 905 b. The core network 925 provides connectivity with other wirelesscommunication systems and wired communication systems. The core networkmay include one or more service subscription databases to storeinformation related to the subscribed wireless devices 910 a, 910 b, 910c, and 910 d. A first base station 905 a can provide wireless servicebased on a first radio access technology, whereas a second base station905 b can provide wireless service based on a second radio accesstechnology. The base stations 905 a and 905 b may be co-located or maybe separately installed in the field according to the deploymentscenario. The wireless devices 910 a, 910 b, 910 c, and 910 d cansupport multiple different radio access technologies.

In some implementations, a wireless communication system can includemultiple networks using different wireless technologies. A dual-mode ormulti-mode wireless device includes two or more wireless technologiesthat could be used to connect to different wireless networks.

FIG. 10 is a block diagram representation of a portion of a radiostation. A radio station 1005 such as a base station or a wirelessdevice (or UE) can include processor electronics 810 such as amicroprocessor that implements one or more of the wireless techniquespresented in this document. The radio station 1005 can includetransceiver electronics 1015 to send and/or receive wireless signalsover one or more communication interfaces such as antenna 1020. Theradio station 1005 can include other communication interfaces fortransmitting and receiving data. Radio station 1005 can include one ormore memories (not explicitly shown) configured to store informationsuch as data and/or instructions. In some implementations, the processorelectronics 1010 can include at least a portion of the transceiverelectronics 1015. In some embodiments, at least some of the disclosedtechniques, modules or functions are implemented using the radio station1005.

It is thus evident that non-orthogonal spreading codes can be used toobtain a larger pool of reference signals. The larger pool of referencesignals can be leveraged to carry control information in pre-configuredtransmissions. The larger pool also reduces the probability of datacollisions in grant-free transmissions, thereby increasing resourceefficiency for IoT scenarios.

From the foregoing, it will be appreciated that specific embodiments ofthe presently disclosed technology have been described herein forpurposes of illustration, but that various modifications may be madewithout deviating from the scope of the invention. Accordingly, thepresently disclosed technology is not limited except as by the appendedclaims.

The disclosed and other embodiments, modules and the functionaloperations described in this document can be implemented in digitalelectronic circuitry, or in computer software, firmware, or hardware,including the structures disclosed in this document and their structuralequivalents, or in combinations of one or more of them. The disclosedand other embodiments can be implemented as one or more computer programproducts, i.e., one or more modules of computer program instructionsencoded on a computer readable medium for execution by, or to controlthe operation of, data processing apparatus. The computer readablemedium can be a machine-readable storage device, a machine-readablestorage substrate, a memory device, a composition of matter effecting amachine-readable propagated signal, or a combination of one or morethem. The term “data processing apparatus” encompasses all apparatus,devices, and machines for processing data, including by way of example aprogrammable processor, a computer, or multiple processors or computers.The apparatus can include, in addition to hardware, code that creates anexecution environment for the computer program in question, e.g., codethat constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, or a combination of one or moreof them. A propagated signal is an artificially generated signal, e.g.,a machine-generated electrical, optical, or electromagnetic signal, thatis generated to encode information for transmission to suitable receiverapparatus.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this document can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Computer readable media suitable for storingcomputer program instructions and data include all forms of non-volatilememory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., EPROM, EEPROM, and flash memorydevices; magnetic disks, e.g., internal hard disks or removable disks;magneto optical disks; and CD ROM and DVD-ROM disks. The processor andthe memory can be supplemented by, or incorporated in, special purposelogic circuitry.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of any invention or of what may beclaimed, but rather as descriptions of features that may be specific toparticular embodiments of particular inventions. Certain features thatare described in this patent document in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

What is claimed is:
 1. A method for wireless communication, comprising:receiving, at a mobile device, a message indicating a set of controloptions available to the mobile device for data transmissions; selectinga spreading code sequence from a number of spreading code sequences,wherein the spreading code sequence corresponds to a control option inthe set of control options, wherein the number of spreading codesequences is greater than a length of each of the spreading codesequence, and wherein the spreading code sequences are generated using afirst method when the length of each of the spreading code sequences isgreater than or equal to a value; generating a plurality of referencesignal symbols using the spreading code sequence; and transmitting, fromthe mobile device, the plurality of reference signal symbols.
 2. Themethod of claim 1, wherein the first method includes generating thespreading code sequences using a Fourier Transform matrix of dimension Nand a permutation of ones and zeros that includes M=1+C_(N) ¹+C_(N) ²+ .. . +C_(N) ^(N-2) vectors, each vector having a length of N.
 3. Themethod of claim 1, wherein the value is equal to
 3. 4. The method ofclaim 1, wherein the spreading code sequences are generated using asecond method different from the first method when the length of each ofthe spreading code sequence is less than the value, wherein the secondmethod includes generating the spreading code sequences by combining 1and a set of primitive Nth roots of unity, N being in a range from 1 tothe number of spreading code sequences.
 5. The method of any of claims 1to 4, wherein the set of control options include information ofmodulation and code schemes, redundancy version, or hybrid automaticrepeat request (HARQ) process index for data transmissions.
 6. Themethod of any of claims 1 to 5, wherein the number of spreading codesequences is equal to or greater than a number of control options.
 7. Amethod for wireless communication, comprising: receiving, at a mobiledevice, a message indicating one or more parameters and a number ofspreading code sequences for data transmissions, wherein the spreadingcode sequences are generated using a first method when the length ofeach of the spreading code sequences is greater than or equal to avalue; generating a reference signal sequence using the one or moreparameters and a spreading code sequence from the spreading codesequences, wherein the number of spreading code sequences is greaterthan the length of each of the spreading code sequence; andtransmitting, from the mobile device, the reference signal sequence. 8.The method of claim 7, wherein the first method includes generating thespreading code sequences using a Fourier Transform matrix of dimension Nand a permutation of ones and zeros that includes M=1+C_(N) ¹+C_(N) ²+ .. . +C_(N) ^(N-2) vectors, each vector having a length of N.
 9. Themethod of claim 7, wherein the value is equal to
 3. 10. The method ofclaim 7, wherein the spreading code sequences are generated using asecond method different from the first method when the length of each ofthe spreading code sequence is less than the value, wherein the secondmethod includes generating the spreading code sequences by combining 1and a set of primitive Nth roots of unity, N being in a range from 1 tothe number of spreading code sequences.
 11. The method of any of claims7 to 10, wherein the one or more parameters indicate a number ofZadoff-Chu roots or a number of cyclic shifts.
 12. The method of any ofclaim 11, wherein generating the reference signal further comprises:generating a legacy reference signal symbol using the one or moreparameters; obtaining a legacy reference signal sequence by repeatingthe legacy reference signal symbol for N times, wherein N is the lengthof each of the spreading code sequence; selecting the spreading codesequence from the spreading code sequences; and multiplying,element-by-element, the legacy reference signal sequence with thespreading code sequence to obtain the reference signal sequence.
 13. Themethod of any of claims 7 to 10, wherein the one or more parametersindicate a legacy reference signal sequence.
 14. The method of claim 13,wherein generating the reference signal further comprises: selecting thespreading code sequence from the spreading code sequences; andmultiplying, element-by-element, at least a part of the legacy referencesignal sequence with the spreading code sequence to obtain the referencesignal sequence.
 15. A method for wireless communication, comprising:transmitting, to a mobile device, a message indicating a set of controloptions available to the mobile device for data transmissions; andreceiving, from the mobile device, a plurality of reference signalsymbols, wherein the plurality of reference signal symbols is generatedusing a spreading code sequence selected from a number of spreading codesequences, wherein the spreading code sequence corresponds to a controloption in the set of control options, wherein the number of spreadingcode sequences is greater than a length of each of the spreading codesequence, and wherein the spreading code sequences are generated using afirst method when the length of each of the spreading code sequences isgreater than or equal to a value.
 16. The method of claim 15, whereinthe first method includes generating the spreading code sequences usinga Fourier Transform matrix of dimension N and a permutation of ones andzeros that includes M=1+C_(N) ¹+C_(N) ²+ . . . +C_(N) ^(N-2) vectors,each vector having a length of N.
 17. The method of claim 15, whereinthe value is equal to
 3. 18. The method of claim 15, wherein thespreading code sequences are generated using a second method differentfrom the first method when the length of each of the spreading codesequence is less than the value, wherein the second method includesgenerating the spreading code sequences by combining 1 and a set ofprimitive Nth roots of unity, N being in a range from 1 to the number ofspreading code sequences.
 19. The method of any of claims 15 to 18,wherein the set of control options include information of modulation andcode schemes, redundancy version, or hybrid automatic repeat request(HARM) process index for data transmissions.
 20. The method of any ofclaims 15 to 19, wherein the number of spreading code sequences is equalto or greater than a number of control options.
 21. A method forwireless communication, comprising: transmitting, to a mobile device, amessage indicating one or more parameters and a number of spreading codesequences for data transmissions, wherein the spreading code sequencesare generated using a first method when the length of each of thespreading code sequences is greater than or equal to a value; andreceiving, from the mobile device, a reference signal sequence, whereinthe reference signal sequence is generated using the one or moreparameters and a spreading code sequence from the spreading codesequences, and wherein the number of spreading code sequences is greaterthan the length of each of the spreading code sequence.
 22. The methodof claim 21, wherein the first method includes generating the spreadingcode sequences using a Fourier Transform matrix of dimension N and apermutation of ones and zeros that includes M=1+C_(N) ¹+C_(N) ²+ . . .+C_(N) ^(N-2) vectors, each vector having a length of N.
 23. The methodof claim 21, wherein the value is equal to
 3. 24. The method of claim21, wherein the spreading code sequences are generated using a secondmethod different from the first method when the length of each of thespreading code sequence is less than the value, wherein the secondmethod includes generating the spreading code sequences by combining 1and a set of primitive Nth roots of unity, N being in a range from 1 tothe number of spreading code sequences.
 25. The method of any of claims21 to 24, wherein the one or more parameters indicate a number ofZadoff-Chu roots or a number of cyclic shifts.
 26. The method of any ofclaims 11 to 24, wherein the one or more parameters indicate a legacyreference signal sequence.
 27. An apparatus for wireless communicationcomprising a processor that is configured to carry out the method of anyof claims 1 to
 26. 28. A non-transitory computer readable medium havingcode stored thereon, the code when executed by a processor, causing theprocessor to implement a method recited in any of claims 1 to 26.